Machine tool

1. A machine tool capable of performing screw-machining on a rotating workpiece, comprising: a tool rest that can attachably and detachably equip a turning tool with an insert on its tip, said tool rest being provided so as to be freely driven to move in first and second axial directions orthogonal to each other, and said tool rest also being provided so as to freely rotate about a third axis orthogonal to said first and second axial directions so as to be positioned at a selected tool-rest angle with respect to the workpiece; input means for inputting machining information corresponding to screw-machining a screw having flank portions comprised of a first flank portion and a second flank portion facing said first flank portion, and a ridge having an angle; a cutting pattern computing portion, which computes a cutting pattern, in which said screw-machining includes rotating said turning tool about the third axis and positioning said turning tool, based on the angle of a ridge shown in the machining information input by said input means; said cutting pattern having different machining processes for performing respective machining concerning said first flank portion and said second flank portion of said screw to be machined on the basis of the angle of said ridge, said machining processes including changing the tool-rest angle without changing the insert; and a screw-machining executing portion executing said screw-machining on said workpiece, said machining processes concerning said first flank portion and said second flank portion performed in an order based on the cutting pattern computed by said cutting pattern computing portion.

2. The machine tool as set forth in claim 1 , wherein said cutting pattern computing portion computes said cutting pattern in such a manner that said turning tool is inverted in machining the first flank and the second flank of said ridge.

3. The machine tool as set forth in claim 1 , wherein said cutting pattern computing portion computes said cutting pattern in such a manner that finish machining for the first flank and the second flank of a ridge are done by a separate process.